I'm currently getting the following error:
 

Create custom text fields called Question and Answer. The Answer field must allow reps to include images and format text that they enter.

I have fields Question (Text field: Question__c) and Answer (Rich Text Area: Answer__c) added to the Linked Article object. 
 

In Trailhead > Reports & Dashboards > Extending Reports using the AppExchange 

I get the the follwoing error message even though the "Wedges" are setup correctly on the "New Trend by Source" Pie Chart.   Images attached showing error message & visual of Pie Chart.
Any input or wisdom would be greatly appreciated. 
Joe Johnson